For example, Patent Literature 1 discloses an anomaly monitoring apparatus for microcomputers that is capable of monitoring the repetitive anomalous operation as well as the sporadic anomalous operation of a microcomputer. This anomaly monitoring apparatus monitors any anomaly in a microcomputer by a watchdog (WD) signal from the microcomputer and further counts the number of times of occurrence of anomalous operation of the microcomputer. As long as the number of times of occurrence of anomalous operation is smaller than a reference number of times, the anomaly monitoring apparatus generates a pulsed reset signal and tries to restore the microcomputer to normal state. Meanwhile, when the number of times of occurrence of anomalous operation exceeds the reference number of times, the anomaly monitoring apparatus generates a reset hold signal and stops the control by the microcomputer.
However, for example, when the controlled object of a microcomputer is a vehicle engine, a problem arises. If the control by the microcomputer is stopped immediately when anomalous operation occurs in the microcomputer more frequently than a reference number of times, the engine is stopped and the vehicle is rendered inoperable. When the operation of the microcomputer becomes anomalous and a reset signal is outputted to the microcomputer but the operation of the microcomputer is not restored to normal state by outputting the reset signal once, the following takes place: the anomaly monitoring apparatus continuously detects the anomalous operation of the microcomputer. For this reason, the microcomputer is not restored to normal state and moreover, there is the possibility that the control of the microcomputer will be stopped. As a result, there is the possibility that an undesirable situation will be contrarily incurred depending on the circumstances in which the vehicle is placed. As mentioned above, holding a reset signal in conventional anomaly monitoring apparatuses is not always sufficient to cope with the anomalous operation of the microcomputer depending on the type of the controlled object.
[Patent Literature 1] JP-A-2004-265322